Journal of Applied Physiology, Vol 59, Issue 4 1208-1213, Copyright © 1985 by American Physiological Society
Changes in antidromic latencies of medullary respiratory neurons in hypercapnia and hypoxia
A. L. Bianchi and W. M. St John
We evaluated mechanisms underlying changes in discharge frequencies of
medullary respiratory neurons. This evaluation was made by determining
variations in antidromic latencies; these variations reflect changes in
membrane potentials. In decerebrate, vagotomized, paralyzed, and ventilated
cats, activities of the phrenic nerve and single respiratory neurons were
monitored in hyperoxic normocapnia, hyperoxic hypercapnia, and/or
normocapnic hypoxia. Axonal projections were defined as bulbospinal or
laryngeal by antidromic activation. At normocapnic hyperoxia, antidromic
latencies fell to minima during periods of spontaneous neuronal activity,
with maxima occurring between neuronal bursts. In hypercapnia or hypoxia,
these minima were not altered, whereas maximum latencies typically rose for
neurons whose discharge frequencies increased. However, the increased
frequencies most strongly correlated with increases in the difference
between maximum and minimum latencies. No such correlation was evident for
neurons whose discharge frequencies declined. We conclude that the overall
change of membrane potential primarily defines neuronal discharge
frequencies. Changes in membrane potentials induced by peripheral and
central chemoreceptor afferents and by direct actions of hypercapnia and
hypoxia are discussed.
